A straightforward but essential check — how long a 500 L tank actually keeps a generator running, and what that costs per hour.
| Fuel tank capacity | 500 L |
| Fuel consumption basis | Per-hour rate (already reflects the expected load point) |
| Consumption rate | 45 L/hr |
| Fuel price | $1.20/L |
| Check | Requirement | Actual | Status |
|---|---|---|---|
| Runtime on a full 500 L tank | n/a (this is the computed result) | 11.11 hours | ✓ PASS |
| Hourly fuel cost | n/a (this is the computed result) | $54.00/hr | ✓ PASS |
Key insight: Fuel consumption rate is deliberately never a built-in constant in this calculator — it varies significantly by genset model, engine size, and load level, so using a generic assumed rate instead of the specific unit's own datasheet figure (or better, a measured value from the actual installation) could meaningfully misstate runtime, which matters directly for life-safety minimum-runtime compliance.
Every input in this example is editable in the live calculator — free, no signup.
Open Genset Fuel Consumption & Running Cost calculator →The calculator also accepts a per-kWh basis, in which case the consumption rate is multiplied by the actual load in kW to get an hourly rate — this matters because a genset's L/kWh efficiency typically varies with load level (often worse at very light or very heavy loads than at its optimal mid-range point), so the per-kWh figure used should match the actual expected operating load, not just an arbitrary reference point.
A facility with an NFPA Class 48 requirement (48-hour minimum runtime) needs either a large enough tank to run 48 hours without refueling, or a documented, reliable refueling plan (fuel supply contract, on-site bulk storage) that can sustain the generator beyond what the day tank alone provides — this runtime calculation is exactly the check that reveals whether the installed tank size alone is sufficient or whether a refueling plan is required.